Mirror assembly for an arc imaging furnace



Nov. 3, 1964 H. 1.. MORIAN, JR

MIRROR ASSEMBLY FOR AN ARC IMAGING FURNACE Filed Feb. 23, 1962 3Sheets-Sheet 1 1964 H. L. MORIAN, JR 3,155,813

MIRROR ASSEMBLY FOR AN ARC IMAGING FURNACE Filed Feb- 23 1962 3Sheets-Sheet 2 F '9' 2 INVENTOR.

Harold L. Moriun,Jr BY At rney Nov. 3, 1964 H. L. MORIAN, JR 3,155,813

MIRROR ASSEMBLY FOR AN ARC IMAGING FURNACE Filed Feb. 23, 1962 5Sheets-Sheet 3 INVENTOR.

Harold L. Moriun,Jr.

/im-d/ i the high temperature flux.

United States Patent 3,155,813 ASEMBLY FGR AN ARC EMAGHNG FURNAKIEHarold L. Marian, fin, Arlington, Mass, assignor to Arthur D. Little,lac, Cambridge, Mass, a corporation of Massachusetts Fair. 23, 11962,der. No. 175,972; 2 Claims. ((3%. 2i9--3S3) This invention relates to anarc imaging furnace and more particularly to an imaging furnace whichincorporates two ellipsoidal projection mirrors and one ellipsoidalreimaging mirror.

There are now available, continuous duty arc imaging furnaces which areconstructed to have two radiant energy sources which are usedalternately to provide a continuous source of high temperature.Conveniently the source of radiant energy is an arc formed between ananode and cathode. Normally the anode of such an arc lamp has a life ofa matter of 20 minutes or so and the cathode 40 minutes or so, whichmeans that it is necessary periodically to change the anode and thecathode if a long period of continuous operation is desired. For examplein the growth of crystals under controlled conditions at very hightemperatures, it is sometimes necessary to operate an imaging furnacefor as much as several hours. it will be appreciated that if one is togrow single crystals in this manner it is necessary to be able to switchfrom one lamp source to another without any interruption in Presentlythe switching from one lamp to another is done by means of a flip-flopmirror which is turned first to face one ellipsoidal mirror and thenanother. This arrangement means that in the switch-over the radiant fluxserving as the source of heat in the imaging furnace is interrupted.This is not desirable, particularly in the growth of single crystals andin some cases, makes the imaging furnace unworkable for this purpose. itwould therefore be desirable to have incoporated in an arc imagingfurnace, an apparatus which would permit the switching from one arc lampto another without any interruption of the radiant flux concentrated inthe working area, for example on the crystal growing apparatus. It wouldalso be desirable to have apparatus of this character which wouldrequire no adjustment once the switching was accomplished, that is tohave an apparatus which would maintain mirrors constantly in alignment.The apparatus of this invention provides such an arrangement.

It is therefore an object of this invention to provide an apparatususable with an arc imaging furnace which permits continuous operation ofthe furnace while providing for replacement of the anode and cathodecarbons. It is another object to provide such an apparatus which permitsswitching from one lamp source to another without any interruption ofthe high temperature flux. it is still another object to provide such anapparatus which does not require continual realignment once originalalignment has been achieved. It is yet another object to provide twoslidably mounted mirrors which can be automatically interchanged andwhich do not interrupt radiant flux in the process of changing lamps andtherefore which do not rely on their operation upon a fast switchingtime. Other objects of the invention will in part be obvious and will inpart be apparent hereinafter.

The invention accordingly comprises the features of construction,combinations of elements and arrangement of parts which will beexemplified in the constructions ice hereinafter set forth and the scopeof the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed descriptions taken inconnection with the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a typical arc imaging furnacein which the mirror assembly of this invention is used;

FIG. 2 is a side elevational view of the mirror assembly; and

FIG. 3 is an end elevational view looking from the forward end.

Briefly, the mirror assembly of this invention comprises a firstreflecting mirror associated with a first projection mirror, a secondreflecting mirror associated with a second projection mirror andadjacent the first reflecting mirror; support means adapted to hold thereflecting mirrors in a fixed and predetermined relationship to eachother and to their respective projection mirrors; elevated horizontalrails associated with the support means; and means for moving thesupport means back and forth along the rails whereby the two projectionmirrors may be alternately used to project radiant energy onto areimaging mirror without interruption in the transmission of the radiantenergy.

The incorporation of the mirror assembly of this invention into atypical arc imaging furnace may be seen with reference to FIG. 1. Themirror assembly itself is indicated within the dotted rectangular area21. It may, however, first be helpful to identify the primary workingparts of an arc imaging furnace to better understand the constructionand function of the mirror assembly.

The are imaging furnace of FIG. 1 has two ellipsoidal projection mirrors10 and 11. In the terminology used in the description which follows theforward end of the mirror assembly will be that which is nearest thechip soidal projection mirror 11, i.e., the right hand mirror whichfunctions with ellipsoidal projection mirror 10. For each of theellipsoidal projection mirrors i and ii there is provided identicalauxiliary equipment. The radiant energy source, generally referred to asthe lamp 12, comprises a cathode 13 and an anode 14 held in spacedrelationship such that when power is applied by means of a power source17, an arc is created across the gap between the cathode and the anodeto furnish the source of radiant energy required. Suitable ellipsoidalprojection mirror supports 18 are provided along with a cathode supportand drive 15 and an anode support and drive 16. Located within the mainmirror supports 18 are alignment screws 19 used to effect an initialalignment of the ellipsoidal projection mirrors. The entire assembly ismounted on a base 20.

A reimaging ellipsoidal mirror 25 is used to focus the radiant energyupon the work area 26 indicated generally as a focal point x. It will ofcourse be appreciated that any of a variety of equipment may be locatedwithin area 26 such as, for example, crystal growing apparatus. Any suchapparatus may be supported along a horizontal support bar 27 which inturn is held in place by a mounting 28. Inasmuch as ellipsoidal mirrors1% 11 and 25, along with their associated equipment as described above,are not part of this invention they need not be further discussed exceptto indicate their relation to the mirror assembly of this invention.

The mirror assembly indicated in the rectangular box it is shown indetail in FIGS. 2 and 3. It will be appreoiated that it is necessary toposition the mirrors 3%) and 31 such that mirror 3% reflects radiantenergy from ellipsoidal mirror lit) to the reimaging mirror 25. Likewisemirror 31 is associated with ellipsoidal projection mirror 11 andperforms a function identical to that of mirror Ell. Because the anodes1 and cathodes l3 burn out, i.e., usually in about 20 minutes for anodesand 40 minutes for cathodes, it is necessary to alternate between thelamps, i.e., first using the left hand lamp focusing upon the forwardmirror 3d and then the right hand lamps with the after mirror Thispermits changing the anodes and cathodes regularly while at the sametime providing .a continuous and constant source of radiant energy atthe focal point 24 associated wi h reimaging mirror 25.

By the apparatus of this invention mirrors 341 .and 31 are alternatelyshifted into position in a manner such that no alignment is requiredonce the original alignment of the mirrors is achieve Moreover, as willbecome apparent the shifting process provides for the continual transferof radiant energy without any interruption. Thus the necessary hightemperatures may be brought to focus upon the focal point x for anextended period of time despite the limitations placed upon the lengthof operation of any one individual anode or cathode in the lamps.

FIG. 2 is a side elevational view of the mirror assembly of thisinvention, while 3 is an end view looking from the forward mirror 11toward the after mirror llll. Focusing mirror all, which in FIG. 2 is infront of focusing mirror 3i, is mounted on a base 32 which has aninclined face, the angle of inclination being that reouired to cause themirror to reflect the radiant energy from mirror ill onto reimagingmirror 2-5 of Phil. 1. This mirror is mounted by means of a mirrorsupport plate as and by screws 33 to the mirror base 32. The mirror isaffixed to the mirror support plate 3 through adjustable clips 33 andheld in position by springs 44 In a similar fashion the reflectingmirror 31 is atfixed to a base 34 with an inclined face. The angleformed by the two inclined faces of bases and 34 will, of course, bedetermined by the optics of the imaging furnace. in the same m nnermirror 31 has a support plate 377 and is afiixed to it throughadjustable clips Likewise springs 41 are provided at the corners of theface of the mirror to hold it firmly to the clips.

The two mirror bases 32 and 34 are affixed to or may be integral withthe housing platform as which has one platform extension 4 forward andtwo platform extensions after. The single platform extension 47 isequipped with a suitable bearing and is adapted to move horizontallyover a bar 1' circular forward rail 53. Likewise the after housingextensions are similarly equippe with bearings Sll and are adapted tomove horizontally over a circular after rail 54-.

The forward rail 53 is in turn permanently positioned in a mounting aswhich is integral with a forward rail support 5'7; and in like fashionthe after rail 5'4 is permanently positioned in a mounting 58 which isintegral with a rail support 5h. It will be appreciated thatthe railsare so affixed in the mounting and support that they do not rotate.

It will be seen in PEG. 3 that through the extensions 47 and St) thehousing platform and hence the llllIIOlS maybe moved back and forth in ahorizontal plane such that they alternately place mirrors Fill and 33.in appropriate positions to reflect radiant energy from ellipsoidalmirrors lit and ill, respectively. In order to affect this horizontalmotion it is necessary to provide apparatus for doing this, theapparatus being such that it may be actuated by forces external of thearc imaging furnace. There is, therefore, provided adrive wheel or. anda wire 63 which is permanently affixed to an extension 64 of the forwardplatform e tension 4'7. By turning drive wheel 62, wire 63 can be madeto pull'the housing platform in either direction. in order to achievethis there are also provided guide relh as which are attached d to therail supports 5'7 by means of suitable attaching support Drive Wheel s2is mounted on a drive shaft 'Til which in turn may be manually driventhrough a cable 71 which is coupled to the shaft 7% by a coupling 72(PEG. 2). The shaft itself is in a housing '74 which is mounted on orintegral with a support '75 which in turn is attached to the mainsupport 2%) of the arc imaging furnace. Alternately, shaft 7d and hencedrive wheel may be turned through the use of a sprocket wheel 7%,mounted on shaft 7d, and a suitable chain 79 for the sprocket Wheel '78.

in the operation of the arc imaging furnace incorporating the mirrorassembly of this invention we may assume first that the left hand lampi2 is f ictioning and that radiant energy is focused onto re mirror 25by means of mirror When the time is reached that anode id or cathode i3is close to bell-lg burned out, right hand lamp ii. is energized, shaftTo is urned mirror is it into position such that it will r "lect radiantenergy now derived the right hand mp and focused from projection :lirrori onto reimging mirror 25. Thus in the changeover of one lamp to anotherthere is no time in the operation when radiant energy is cut off fromthefocal area 126. Moreover by the poper original alignment of mirrors 3'?and 3.; onto their respective bases 32 and 34 no realignment is requiredwhen the mirrors are alternately shifted into position. This obviouslymakes for elficient and continuous operation of the arc imaging furnace.

It will thus be seen that the objects set forth above among these madeapparent from the preceding description are eiliciently attained andsince certain changes may be made in the above constructions withoutdeparting from the scope of the invention it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

I claim:

1. An arc imaging furnace, comprising (a) duplicate first and secondellipsoidal projection mirrors;

(b) duplicate first and second radiant energy source positioned withrespect to said projection mirrors to irect radiant energy onto saidfirstand second ellipsoidal projection mirrors, respectively;

(0) a .reiin'rging ellipsoidal mirror adapted to concentrate radiantenergy upon a Work area, said reimaging mirror being located above theplane of said projection mirrors and centrally positioned between them;

(d) duplicate first second reflecting mirrors positioned between saidlil'Si. and second projection mirrors and aligned therewith, said firstand second reflecting mirrors being adjacent to each other and beingadapted to alternate in directing said radiant energy first from saidfirst ellipsoidal projection mirror and then from said secondellipsoidal mirror onto said reimaging ellipsoidal mirror;

(e) mirror support means adapted to hold said firs and second reflectingmirrors in fixed angular relationship to each other, in radiant energyreceiving relationship alternately with said first and secondellipsoidal projection mirrors, respectively, and alternately in radiantenergy directing relationship with said reimaging mirror;

('f) horizontal rails adapted to support and furnish direction ofmovement to said mirror support means; and

(g) means for moving said mirror support means back and forth along saidrails whereby first and second reflecting mirrors are movablewithrespect to said ellipsoidal projection mirrors and said roll-.-

aging mirror and are capable in the' alternating movement of supplyingsaid radiant energy constantly and continuously to said work area.

2. Mirror assembly in accordance with claim 1 wherein said means formoving said mirror support means comprises a rotatable drive wheel andshaft means for rotating said drive Wheel.

References Cited in the file of this patent UNITED STATES PATENTS1,278,026 Salto Sept. 3, 1918 6 Bowen Feb. 18, 1936 Walker Dec. 5, 1950Staples Jan. 30, 1951 Walker Apr. 3, 1951 Wendelken Mar. 1, 1960 LoZieret a1 Sept. 19, 1961 Chellis et al Sept. 10, 1963

1. AN ARC IMAGING FURNACE, COMPRISING (A) DUPLICATE FIRST AND SECONDELLIPSOIDAL PROJECTION MIRRORS; (B) DUPLICATE FIRST AND SECOND RADIANTENERGY SOURCES POSITIONED WITH RESPECT TO SAID PROJECTION MIRRORS TODIRECT RADIANT ENERGY ONTO SAID AND SECOND ELLIPSOIDAL PROJECTIONMIRRORS, RESPECTIVELY; (C) A REIMAGING ELLIPSOIDAL MIRROR ADAPTED TOCONCENTRATE RADIANT ENERGY UPON A WORK AREA, SAID REIMAGING MIRROR BEINGLOCATED ABOVE THE PLANE OF SAID PROJECTION MIRRORS AND CENTRALLYPOSITIONED BETWEEN THEM; (D) DUPLICATE FIRST AND SECOND REFLECTINGMIRRORS POSITIONED BETWEEN SAID FIRST AND SECOND PROJECTION MIRRORS ANDALIGNED THEREWITH, SAID FIRST AND SECOND REFLECTING MIRRORS BEINGADJACENT TO EACH OTHER AND BEING ADAPTED TO ALTERNATE IN DIRECTING SAIDRADIANT ENERGY FIRST FROM SAID FIRST ELLIPSOIDAL PROJECTION MIRROR ANDTHEN FROM SAID SECOND ELLIPSOIDAL MIRROR ONTO SAID REIMAGING ELLIPSOIDALMIRROR;